Field of the Invention
The present disclosure relates to an ultrasonic apparatus that acquires information of a subject using an ultrasonic wave.
Description of the Related Art
In recent years, photoacoustic tomography (PAT) has been proposed as an optical imaging technology. When a measurement light, such as a pulsed laser, is irradiated to a subject, an acoustic wave is generated while the measurement light is absorbed inside the subject. The above phenomenon is referred to as a photoacoustic effect, and the acoustic wave generated with the photoacoustic effect is referred to as photoacoustic wave.
Since the absorption coefficient of the light energy is different in the tissues constituting the subject, the generated sound pressures of the photoacoustic waves are different. In photoacoustic tomography, the generated photoacoustic wave is detected with transducers, and by analyzing the received signal, information related to the optical characteristics inside the subject can be formed into an image.
Meanwhile, ultrasonic imaging is known as a method of acquiring structural information inside the subject. In ultrasonic imaging, ultrasonic waves are transmitted to the subject from a plurality of ultrasonic wave transducers disposed in a probe, and reflected wave generated at interfaces with different acoustic impedances are received and analyzed. With the above, information (structural information) related to the sound characteristic of the subject can be formed into an image.
An apparatus that combines the above technique, in which light is irradiated to an ultrasonic wave generating member disposed external to the subject to generate a photoacoustic wave (an ultrasonic wave) is desired. In such an apparatus, the above photoacoustic wave is used to perform ultrasonic imaging. Such a technique is referred to as a photoacoustic induced ultrasonic imaging apparatus so as to distinguish the apparatus from a typical pulse-echo ultrasonic imaging that uses an ultrasonic wave electrically generated with an acoustic wave (ultrasonic wave) transmitting element as a transmission wave.
Non-patent literature “Four dimensional hybrid ultrasound and optoacoustic imaging via passive element optical excitation in a hand-held probe Appl. Phys. Lett. 105, 173505 (2014)” describes a photoacoustic induced ultrasonic imaging apparatus that uses a microsphere light absorbing member as an ultrasonic wave generating member.
In a typical pulse-echo ultrasonic imaging apparatus that includes a plurality of transducers that transmit ultrasonic waves, the intensity distribution of the ultrasonic waves irradiated to the subject can be changed optionally by changing the voltage of each transducer.
On the other hand, with the method described in the non-patent literature, the intensity distribution of the ultrasonic waves cannot be adjusted.